Although nanoparticles have been found to be effective in delivery to more traditional vascularized organs and tissues, there are different challenges for nanoparticle transport in tissues that lack a vascular system to assist in penetration into the tissue. Here we propose a systematic approach to the design of nanomaterials systems that are capable of deep penetration and delivery of agents into avascular tissues. The proposed work will focus on establishing sets of materials design concepts to enhance transport into and through these tissues based on size, charge density and presentation, targeting and dynamic materials chemistries. In the Aim 1, we will develop two promising families of multivalent drug nanocarriers with modular design, each presenting unique advantages for tissue penetration. The transport of these nanocarriers will then be examined as a function of size and charge using ex vivo tissue models to rapidly screen libraries of nanocarriers and identify optimal size/charge characteristics for tissues of interest. We will examine transport in three unique avascular tissue types: cartilage, meniscus and cornea to understand similarities or differences in design requirements and optimal transport characteristics for a range of avascular tissue types. Further translation of this Aim is anticipated to provide fundamental knowledge regarding how to address other similar barrier tissues in the context of drug delivery. Treatment of cartilage to address conditions such as osteoarthritis presents a particularly important medical challenge, and is the disease focus for the later Aims of these studies; however, successful demonstration of this system in the first Aim will be applicable to other tissues and conditions, including delivery to the cornea and joint meniscus. To enable a more tissue-responsive delivery approach, both pH responsive and enzyme degradable linkers will be examined in Aim 2 for the conjugation of therapeutics, with the focus on conjugation of IGF-1, a growth factor that can facilitate cartilage regeneration in early stage osteoarthritis. Optimized versions of the nanocarriers will be studied in an established in vivo using an early surgical trauma rat model to evaluate the efficacy of IGF-1 treatments with the nondegradable, hydrolytic, and protease-activated degradable linkers and determine in vivo real-time pharmacokinetics versus free IGF-1. Cartilage treatment studies will be carried out in this model for IGF-1 delivery. Finally, an additional aspect of this study will be the design of nanoconjugates that release drug selectively to regions of tissue matched to the different nanocarrier transport properties determined in earlier Aims, including degree of penetration and residence time within the tissue. Combination treatments for small molecule drugs including dexamethasone and TLR4 inhibitors will be conjugated to carriers optimal for each drug, in combination with the top IGF-1 formulation. We will evaluate the therapeutic effects of the combinations in a cytokine-challenged ex vivo cartilage tissue model by measuring inflammatory markers, matrix deposition and maintenance, and kinetics of cartilage repair. 1